“We’ve heard from you that there are times when you want additional safeguards,” said Facebook in a blog posting. “Perhaps when discussing private information like an illness or a health issue with trusted friends and family, or sending financial information to an accountant.”
End-to-end encryption will allow you to carry on one-to-one conversations with a single person on just one device. For example, you could strike up what Facebook calls a “Secret Conversation” with a friend, and they would only be able to view that message on the first enrolled device that they open it from. So if a friend were to open your message on their smartphone, they wouldn’t be able to view that same message on their laptop or tablet.
Using technology from Open Whisper Systems (also used in Facebook’s WhatsApp) the sender of a message can even set their own “self-destruct” timer that will vaporize the message after a set period of time. So if you want to go old school like Mission Impossible, you could set it for five seconds. Or if you want to be more generous and provide more time for a message to be read, that option is available. Facebook describes in its white paper for Secret Conversations [PDF]:
Both devices automatically hide messages that specify a timeout once the message timeout has elapsed. The actual deletion of message plaintext from local storage occurs shortly after each message has expired in order to enable abuse reporting in the interim.
At this time, Secret Conversations are only being rolled out on a “limited basis” as Facebook gets its bearings with the new functionality. For users that find the feature enabled on their accounts, be forewarned that it does not currently support GIFs, videos or other rich content.